import torch.nn as nn


def build_act_layer(act_layer):
    if act_layer == "ReLU":
        return nn.ReLU(inplace=True)
    elif act_layer == "SiLU":
        return nn.SiLU(inplace=True)
    elif act_layer == "GELU":
        return nn.GELU()

    raise NotImplementedError(f"build_act_layer does not support {act_layer}")


def build_norm_layer(
    dim, norm_layer, in_format="channels_last", out_format="channels_last", eps=1e-6
):
    layers = []
    if norm_layer == "BN":
        if in_format == "channels_last":
            layers.append(to_channels_first())
        layers.append(nn.BatchNorm2d(dim))
        if out_format == "channels_last":
            layers.append(to_channels_last())
    elif norm_layer == "LN":
        if in_format == "channels_first":
            layers.append(to_channels_last())
        layers.append(nn.LayerNorm(dim, eps=eps))
        if out_format == "channels_first":
            layers.append(to_channels_first())
    else:
        raise NotImplementedError(f"build_norm_layer does not support {norm_layer}")
    return nn.Sequential(*layers)


class to_channels_first(nn.Module):

    def __init__(self):
        super().__init__()

    def forward(self, x):
        return x.permute(0, 3, 1, 2)


class to_channels_last(nn.Module):

    def __init__(self):
        super().__init__()

    def forward(self, x):
        return x.permute(0, 2, 3, 1)
